1. Field of Invention
The present invention relates generally to a method of searching for the touch point of a clutch and, more particularly, to a technology that is capable of accurately maintaining the touch point of a dry clutch that is used in a double clutch transmission (DCT) that is mounted on a vehicle.
2. Description of Related Art
A DCT includes a clutch that is capable of automatically transmitting or blocking power using an actuator. When the clutch is a dry clutch, a touch point, that is, a point from which the clutch starts to operate, varies because of a change in the temperature of the clutch or the abrasion of the clutch, and thus it is necessary to appropriately adjust the touch point in order to maintain the reliable operability of the clutch.
FIG. 1 is a graph showing clutch torque characteristics for the strokes of a clutch actuator. When a stroke increases and then encounters a touch point, clutch torque actually starts to increase. If a clutch is in a normal state, the state in which the maximum clutch torque that is designed to be higher than the maximum engine torque that can be transmitted by an engine at the maximum stroke can be transmitted is entered. In contrast, if the touch point is moved because of a change in the temperature of the clutch or the abrasion of the clutch, the maximum torque of an engine is not sufficiently transmitted in the case of the maximum stroke.
As described above, the touch point is a factor that is related to the continuous and stable maintenance of the relationship of control between the clutch actuator and the clutch. FIG. 2 illustrates a conventional method of searching for and setting the touch point of a clutch. This method is performed when a vehicle is stopped or when a gearbox is in a neutral state immediately after the cranking of an engine.
That is, in the conventional method, the clutch actuator is manipulated from a location where the clutch is not engaged toward a location where the clutch is disengaged (“A”), the location of a clutch actuator from which the clutch starts to be rotated (“B”) is determined to be a touch point, this location is set as a new touch point (“C”), and the clutch actuator is manipulated based on the newly set touch point.
However, the above-described conventional method is problematic in that changes in the characteristics of the touch point that occur while a vehicle is being driven cannot be taken into consideration because the touch point can only be learned while a vehicle is stopped.
The above description of the technologies is merely provided to help understand the background of the present invention. However, the above description of the technologies should not be construed as admitting that those technologies correspond to prior art that has been known to those having ordinary knowledge in the technical field.